(1) Field of the Invention
The present invention relates to a process for the preparation of alkyleneamines. More particularly, it relates to a process for preparing an alkyleneamine by using a niobium-containing substance as a catalyst.
(2) Description of the Related Art
As means for preparing alkyleneamines, especially ethyleneamines which are industrially important, there can be mentioned a process in which ethylene dichloride is reacted with ammonia. According to this process, amounts formed of piperazine and a piperazine ring-containing cyclic ethyleneamine are small, that is, the non-cyclic ratio is high, and an ethyleneamine having an industrially preferable quality can be obtained. Accordingly, this process is widely carried out. However, in this process, a large quantity of sodium chloride is formed as a by-product and expenses are necessary for separation and treatment of this sodium chloride.
Furthermore, a process for preparing an ethyleneamine by reacting monoethanolamine as the starting material with ammonia in the presence of hydrogen and a hydrogenation catalyst is widely worked. Although ethylenediamine can be efficiently prepared according to this process, since a large quantity of a piperazine ring-containing cyclic ethyleneamine, which is not preferred from the viewpoint of quality, is inevitably formed, it is difficult to obtain a polyethylene-polyamine having a high molecular weight.
U.S. Pat. No. 3,714,259 proposes a process in which a polyethylene-polyamine is prepared by carrying out the liquid phase reaction between ethylenediamine and ethanolamine in the presence of a hydrogenation catalyst such as Ni, Cu or Cr in a hydrogen gas atmosphere. According to this process, only a lower polyethylene-polyamine such as diethylenetriamine is formed and a higher polyethylene-polyamine such as tetraethylenepentamine or pentaethylenehexamine cannot be obtained. Furthermore, if the reaction is carried out under conditions where the conversion of the starting compound is sufficiently increased, the amount formed of a cyclic polyethylene-polyamine which is not preferred in view of quality, such as piperazine or aminoethylpiperazine, is increased, and a polyamine compound having a hydroxyl group in the molecule is formed.
In addition to the foregoing processes, there is proposed a process for preparing ethyleneamines by reacting monoethanolamine in the presence of a phosphorus-containing substance as the catalyst. For example, Japanese Unexamined Patent Publication No. 51-147,600 discloses a process using phosphoric acid or phosphorous acid as the catalyst. However, since the catalyst of this type is dissolved in a reaction liquid containing water, a special operation is necessary for separating and recovering the catalyst. As means for eliminating this disadvantage, a process using a phosphate or supported phosphoric acid as a catalyst, which is insoluble in a reaction liquid containing water, is proposed. For example, U.S. Pat. No. 4,448,997 teaches a process for the preparation of ethyleneamines where aluminum phosphate is used as a catalyst, and Japanese Unexamined Patent Publication No. 60-41,641 , which corresponds to U.S. Pat. No. 4,463,193 discloses a process for preparing ethyleneamines where a phosphoric acid salt of a metal of the group IIIb such as lanthanum phosphate is used as a catalyst. Furthermore, Japanese Unexamined Patent Publication No. 59-150,538 , which corresponds to U.S. Pat. No. 4,640,822, discloses a process using as a catalyst phosphoric acid supported on titanium dioxide or the like. However, these phosphate and supported phosphoric acid catalysts have an activity lower than free phosphoric acid and it is impossible to prepare a polyethylene-polyamine efficiently. Moreover, when the phosphate or supported phosphoric acid catalyst is used, it is impossible to reduce the content of a piperazine ring-containing cyclic amine which is not preferred from the viewpoint of quality or a hydroxyl group-containing amine such as aminoethylethanolamine to an industrially satisfactory level.
As means for overcoming the defects of these phosphorus-containing catalysts, there can be mentioned a process using a phosphorus-containing ion exchange resin as a phosphorus catalyst having an enhanced activity, as disclosed in Japanese Unexamined Patent Publication No. 57-74,331. However, this catalyst has poor heat resistance and catalyst life.
Silica-alumina catalysts are disclosed in Japanese Unexamined Patent Publication No. 55-38,329 and Japanese Unexamined Patent Publication No. 60-156,651 , which corresponds to U.S. Pat. No. 4,547,591 as non-phosphorus catalysts, but these catalysts have extremely low activity. Accordingly, in the latter patent publication, phosphoric acid is added as an assistant to increase the catalyst activity.
Various processes for preparing alkyleneamines have been proposed as pointed out hereinbefore, but these processes have the following problems.
(1) In the case of a liquid catalyst, the operation of separating and recovering the catalyst from a formed polyamine after termination of the reaction is necessary, and this operation is complicated and a separating equipment is necessary. Accordingly, a solid catalyst is preferred from the industrial viewpoint.
(2) Solid catalysts proposed in the past have a poor activity. Furthermore, in the presence of water, partial decomposition is caused at high temperatures and the activity is degraded with the lapse of time.
(3) In the case of a phosphorus type supported solid catalyst, when active sites are exposed to high temperatures in the presence of water, they are liable to separate from the surface of the carrier. Accordingly, the activity is reduced with the lapse of time and in order to maintain the reactivity, it is necessary to elevate the reaction temperature extremely. This leads to an increase of the reaction pressure.
Especially, in a process for preparing alkyleneamines from alkanolamines as the starting substance, development of a technique of preparing an alkyleneamine having a high non-cyclic ratio and a high quality by using a solid catalyst having a high activity and a high heat resistance, which is not or only slightly soluble in a reaction liquid, is eagerly desired.